Nails and similar such driven fasteners (brads, spikes, staples, screws and the like) have long been utilized for fastening, including fastening combinations of wood and other materials such as plastic, metal composites and resinous materials. Such fasteners have been and will continue to be made of a variety of materials and in a variety of shapes and sizes to meet the needs of a wide range of applications. Powered nailers (gas and pneumatic) have been introduced to enhance worker productivity and enhance ease of nail installation.
Nails are easily as difficult to remove as they are to install. Over time, such fasteners are subject to wide variations in local conditions that change the bond between the nail and host material. Moreover, coatings and shank configurations have been increasingly utilized to maximize withdrawal resistance. Thus, hundreds, and often thousands, of pounds of force are required to withdraw nails from wood (the most common host material). Heretofore, the most common removal tools have been hand tools with claws that either hook under fastener heads or grip their shanks to enable the fasteners to be pried from the host material.
More recently, devices utilizing pneumatic nailer technology have been introduced for removal of nails (see, for example, U.S. Pat. Nos. 5,141,205 and Des. 336,026). In operation these devices (often referred to as “denailers”) receive a portion of a nail protruding from a surface in a bore for straightening and subsequent impact removal utilizing a drive pin extendable through and from the bore. These devices have been successful where the tool bore and pin size (diameter and length) are well matched to the nail size. However, when not well matched, nail displacement may be relatively inefficient.
For a given driving force, it has been found that nail displacement per impact is improved dramatically where drive pin diameter more closely matches the diameter of the nail shank. Therefore, a denailer with considerably more driving force and a large drive pin diameter may not perform well on smaller nails. In addition, prior to impact, the specific distance the nail protrudes into the tool bore affects the eventual distance the nail is displaced. In one tool model tested, a nail protrusion of 16 mm produced greater nail displacement than smaller or larger insertion distances. Finally, during impact the drive pin flexes inside the guide bore which braces the pin. Buckling and bending stresses on the drive pin increase dramatically when protruding outside the bore, and increase as the protruded and unbraced length of the drive pin increases. Heretofore known denailers establish the bore and pin length (and thus protrusion distance) for all cases, thereby subjecting the driver to such buckling stresses even in applications where driver pin protrusion is not needed at all.
Most heretofore known and/or utilized powered denailers are currently configured so that the driver pins protrude from the tool during operation. Given the forces involved, safety considerations would dictate improvement here. Providing a trigger locking device linked to contact with the host material has heretofore proven difficult due to likely interference with nail-straightening operations and/or difficult or crowded work surfaces. One heretofore known tool provided a trigger lock that required user activation. Typically, users either forget to, or choose not to, use this lock routinely. Another manufacturer has provided a spring-loaded secondary trigger that flips into place after the primary trigger is released, locking the primary trigger passively until the secondary trigger is first depressed. In the field it has been observed that the secondary trigger, almost without exception, has been removed or disabled by users.
As may be appreciated from the foregoing, further improvement in powered denailer devices could thus still be utilized, particularly addressing driver durability, flexibility of tool utilization in the field, and safety concerns.